Update tests to work with latest Flask and Werkzeug

[jwag956]

• test client cookie handling completely changed - a new API was introduced
• URL encoding was changed - so many URLs are no longer encoded - tests needed to change.

Bump requirements to latest Flask and Werkzeug - too much work to support older versions (tests mostly). Bump requirements_low to latest - too much effort to keep tests working.

Sigh - mistakenly pushed most of this to master....

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (667c655) 97.52% compared to head (ff34daa) 97.52%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #792 +/- ## ======================================= Coverage 97.52% 97.52% ======================================= Files 34 34 Lines 4453 4453 ======================================= Hits 4343 4343 Misses 110 110 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.